1. Field of the Invention
The present invention relates to a semiconductor nonvolatile memory such as an electrically programmable read-only memory (hereinafter referred to as “EPROM”), particularly to a trimming technique for output characteristic control and redundancy repair of a memory chip built-in circuit.
2. Description of the Related Art
Semiconductor nonvolatile memories such as EPROM are widely utilized as a memory for a portable device and the like because electric power is not required to retain storage information. Recently, as memory cells become finer, update of the memory cell, optimal control of a read condition, and redundancy repair become important in order to improve reliability and a yield of the memory. The update of the memory cell, the optimal control of the read condition, and the redundancy repair are realized by referring to trimming and redundant information during a memory operation. The trimming and redundant information is previously stored in the memory chip, and specifies voltage and current supplied to a built-in circuit, the presence/absence of redundancy line activation, and a substitute address. For example, as disclosed in Japanese Patent Application Laid-Open No. 11-17010, laser fuse trimming is usually performed as a method of storing the trimming and redundant information.
In the method disclosed in Japanese Patent Application Laid-Open No. 11-17010, a fuse element is used to store information. For example, the fuse is selectively cut in a wafer test process, and a logic signal of “0” or “1” is generated as information on the presence/absence of the cutting during the memory operation.
However, in the laser fuse trimming disclosed in Japanese Patent Application Laid-Open No. 11-17010, because the trimming and redundancy (repair) information cannot be updated after package assembly, all the memory chips become defect, when a memory area which needs repair is generated in the test process after the assembly, or when output characteristics of the built-in circuit are shifted in the memory chip. Furthermore, a dedicated mask is required to mount the fuse element, which results in that production cost is increased by the dedicated mask.